package edu.princeton.cs.algs4;


import edu.princeton.cs.stdlib.In;
import edu.princeton.cs.stdlib.StdOut;

/*************************************************************************
 * Compilation: javac DepthFirstDirectedPaths.java Execution: java
 * DepthFirstDirectedPaths G s Dependencies: Digraph.java Stack.java
 * 
 * Determine reachability in a digraph from a given vertex using depth first
 * search. Runs in O(E + V) time.
 * 
 * % tinyDG.txt 3 3 to 0: 3-5-4-2-0 3 to 1: 3-5-4-2-0-1 3 to 2: 3-5-4-2 3 to 3:
 * 3 3 to 4: 3-5-4 3 to 5: 3-5 3 to 6: not connected 3 to 7: not connected 3 to
 * 8: not connected 3 to 9: not connected 3 to 10: not connected 3 to 11: not
 * connected 3 to 12: not connected
 * 
 *************************************************************************/

public class DepthFirstDirectedPaths {
	private boolean[] marked; // marked[v] = true if v is reachable from s
	private int[] edgeTo; // edgeTo[v] = last edge on path from s to v
	private final int s; // source vertex

	public DepthFirstDirectedPaths(Digraph G, int s) {
		marked = new boolean[G.V()];
		edgeTo = new int[G.V()];
		this.s = s;
		dfs(G, s);
	}

	private void dfs(Digraph G, int v) {
		marked[v] = true;
		for (int w : G.adj(v)) {
			if (!marked[w]) {
				edgeTo[w] = v;
				dfs(G, w);
			}
		}
	}

	// is there a directed path from s to v?
	public boolean hasPathTo(int v) {
		return marked[v];
	}

	// return path from s to v; null if no such path
	public Iterable<Integer> pathTo(int v) {
		if (!hasPathTo(v))
			return null;
		Stack<Integer> path = new Stack<Integer>();
		for (int x = v; x != s; x = edgeTo[x]) {
			path.push(x);
		}
		path.push(s);
		return path;
	}

	public static void main(String[] args) {
		In in = new In(args[0]);
		Digraph G = new Digraph(in);
		// StdOut.println(G);

		int s = Integer.parseInt(args[1]);
		DepthFirstDirectedPaths dfs = new DepthFirstDirectedPaths(G, s);

		for (int v = 0; v < G.V(); v++) {
			if (dfs.hasPathTo(v)) {
				StdOut.printf("%d to %d:  ", s, v);
				for (int x : dfs.pathTo(v)) {
					if (x == s)
						StdOut.print(x);
					else
						StdOut.print("-" + x);
				}
				StdOut.println();
			}

			else {
				StdOut.printf("%d to %d:  not connected\n", s, v);
			}

		}
	}

}
